The need for a safe, pollution-free, highly flexible power generation technology has caused increasing interest in fuel cells.
Fuel cells were invented in 1839 by Sir William Grove. A fuel cell is an electrochemical device which directly combines a fuel and an oxidant such as hydrogen and oxygen to produce electricity and water. It has an anode or fuel electrode and a cathode or air electrode separated by an electrolyte. Hydrogen is oxidized to hydrated protons on the anode with an accompanying release of electrons. At the anode, oxygen reacts with protons to form water, consuming electrons in the process. Electrons flow from the anode to the cathode through an external load, and the circuit is completed by ionic current transport through the electrolyte.
Fuel cells do not pollute the environment. They operate quietly, and high temperature fuel cells have a potential efficiency of ca. 80 percent. Virtually any natural or synthetic fuel from which hydrogen can be extracted--by steam reforming, for example--can be employed.
Of current interest because they do not have the handling problems of liquid fuel cell electrolytes are solid oxide fuel cells (SOFC'S) which have a solid, stabilized-zirconia electrolyte and operate at a temperature of 1000.degree. C. While efficient, reliable solid oxide fuel cells are available, the cost per kilowatt of electricity generated by those SOFC'S is presently too high for most commercial applications. The high cost of the cells is due in part to the specialized processes used for cell fabrication, which are relatively slow and expensive. High SOFC cost is also related to the materials problems associated with the conventional SOFC operating temperature of.apprxeq. 1000.degree. C.
Many studies have been made of SOFC electrolyte materials with higher conductivity than the conventional yttria-stabilized zirconia (YSZ). These materials would permit SOFC operation at lower temperatures, 600.degree. to 800.degree. C. It has also been suggested that a SOFC with a thin film YSZ electrolyte could operate efficiently in this temperature range. In addition to allowing lower operating temperatures, thin film SOFC's could be produced at lower cost if a satisfactory large-scale thin film deposition technique were available.